1. Technical Field
The present disclosure relates to an electricity storage device that stores electricity by trapping electrons in an electricity storage layer.
2. Description of the Related Art
In recent years, the awareness of global environmental issues has increased and therefore the creation and use of energy that has a less negative impact on the environment have been required for the purpose of building a sustainable society. Solar and wind power generation techniques are attracting much attention as techniques for creating clean energy. On the other hand, the advance of electricity storage techniques such as secondary batteries and capacitors is expected from the viewpoint of effectively using created energy.
In particular, in the automotive field, the practical use of hybrid and electric vehicles driven by electric motors powered by secondary batteries is being encouraged for the purpose of ensuring energy sources alternative to dwindling fossil fuels and the purpose of reducing the emission of harmful substances such as carbon dioxide. However, the hybrid and electric vehicles have a problem that the hybrid and electric vehicles have a shorter cruising distance as compared to conventional gasoline vehicles. Therefore, the manufacture of secondary batteries with high charge-discharge capacity is expected for the purpose of increasing the cruising distance.
In the mobile device field, secondary batteries with high charge-discharge capacity are required for the purpose of increasing the available time of devices because power consumption is increased due to improved functions. Furthermore, the development of high-capacity capacitors is encouraged for the purpose of storing the energy produced by solar or wind power generation.
Lithium ion batteries and lithium ion capacitors are cited as prime candidates for secondary batteries and capacitors capable of achieving high capacity. However, a current lithium ion battery and lithium ion capacitor have low charge-discharge capacity and therefore the cruising distance of, for example, an electric vehicle equipped with the lithium ion battery or capacitor is very short, about 100 km. An electrolytic solution for use in lithium ion batteries or lithium ion capacitors is liquid, therefore may possibly leak, and has a problem with safety. All-solid-state lithium secondary batteries containing a solid electrolyte instead of an electrolytic solution are under development; however, high capacity has not been attained. Furthermore, these batteries have a problem with high manufacturing costs.
Under such circumstances, a solid-state semiconductor electricity storage device different in operating principle from lithium ion batteries or capacitors has been recently proposed (refer to International Publication No. WO 2012/046325, International Publication No. WO 2013/065093, and the like). The electricity storage device includes an electricity storage layer containing an n-type metal oxide semiconductor particles coated with an insulating material. The operating principle of the electricity storage device is that a new energy level is formed in the electricity storage layer by ultraviolet irradiation and electricity is stored by trapping electrons in the energy level.
The electricity storage device is excellent in safety and can be stably operated because the electricity storage layer is made of an inorganic material. The electricity storage device is simple in manufacture and therefore can be manufactured at low cost. Furthermore, it has been suggested that the capacity per unit volume can be significantly increased by stacking such electricity storage devices (refer to International Publication No. WO 2013/153603).